German Patent No. 23 04 464 describes an electrochemical gas having an electrode made of gold or silver which does not catalyze the establishment of equilibrium of the gas mixture, and which acts together with an electrode made of platinum which catalyzes the establishment of equilibrium in the gas to be measured (the measuring gas). The catalytically inactive electrode materials have the effect that, between the oxygen and the oxidizable or reducible gas components, respectively, a competitive reaction takes place at the electrode. Even with adjusted high lambda values, this causes the free oxygen carried along in the measuring gas hardly to react with, for example, C3H6 or CO, so that free oxygen as well as C3H6 or CO, respectively, reach the three-phase boundary at the catalytically inactive electrode. However, such a gas sensor has a considerable cross sensitivity to the oxygen also present in the gas mixture.